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Can Ballistic Parachute Recovery Systems be safely deployed in a storm?
Suppose the plane is in a thunder storm, and the pilot loses control of the airplane. Would deploying the ballistic parachute be a safe option? Meaning, is it likely that everyone would come out alive? Assume that as soon as the plane hits the ground at a reasonable speed the occupants are safe(as in, there's no ocean to drown in). Has this ever been done before?

It's worth a try considering the alternative.

I thought you have done that with personal parachute out of a 727? The fact is trying to avoid such severe storm is cheaper, safer and more effective thab parachute the whole plane down.

CAPS deployment is unsafe by definition.

@GdD I don't think it is. Don't they have a perfect safety record within certain specified parameters? By unsafe I mean >10% chance of death.

Manufacturers are going to have different opinions of this scenario, but this answer follows the opinion of Cirrus Aircraft in their flight manuals and CCIP syllabi for the SR2X airplanes.
First off, your best bet is to obtain a proper weather briefing prior to departure and obtain in-flight weather updates enroute so you can stay out of a thunderstorm in the first place.  The CAPS has very specific guidelines for operations as well as a maximum demonstrated safe deployment speed, depending of the model of aircraft.  The flight manuals for the SR2X aircraft all state that:
"However because the CAPS is expected to result in structural damage to the airframe and, depending upon adverse external factors such as high deployment speeds, low altitude, rough terrain and high winds, the CAPS deployment may result in severe injury or death to the occupants and its use should not be taken lightly".
Barring that and you actually enter a thunderstorm which is so severe that it either causes departure from controlled flight or structural failure, there is a clause in the CAPS literature stating that if an accident is imminent, even if the acitivation of the CAPS is outside the demonstrated safe deployment range, it should be utilized and activated nonetheless.  The reason has to do with minimizing the amount of energy on impact and even a partially deployed or damaged CAPS is going to slow the aircraft considerably, increasing your chances of survival.
Bottom line is that you did something stupid vis a vis a serious lack of judgment where a safe recovery is no longer possible.  Whatever happens in the next few minutes is probably going to hurt really bad; the only thing we can do is make every effort to minimize how badly we are hurt and minimize the chances that we are going to be killed.  Even an unsafe CAPS deployment in this situation is better than riding down to impact without.

That's good research, but in the end (as the OP doesn't ask for "is it safer than", but "is it safe"), if Cirrus says the CAPS deployment may result in severe injury or death to the occupants, the answer to the question Can Ballistic Parachute Recovery Systems be safely deployed in a storm? must be: Deploying the CAPS, regardless of the conditions, is not safe.

No, it's like any other piece of safety equipment.  It has been demonstrated to reduce the risk of injury or death, but there is no guarantee that injury or death won't happen if it is used.  In a similar vein, automobile airbags can save lives in accidents but there is no guarantee that serious injury or death in an accident won't happen even if the airbag deploys successfully.

In contrast, consider the success rate of another emergency egress aircraft system: The ACES II ejection seat USAF reports that in envelope success rate of ACES II is 94.4%, and combined in envelope and out of envelope success rate is 89.9%.
Out of envelope means the seat was employed in conditions it hasn't been certified for.
Success means the pilot lived, not necessarily uninjured.
So, first consider that these sorts of emergency parachute systems are not a 'safe' option, they're just considered better than guaranteed death.
As for the BPRS, it is not a 'safe' option under any circumstance. It is quite possible that the chute lines could get tangled up in the aircraft - remember that it will be deployed into a powerful wind, and in the event of structural failure, say a wing coming off, the aircraft might be spinning as it falls, tangling the chute lines.
Consider the fate of Vladimir Komarov, test pilot, aeronautical engineer, and cosmonaut. Faced with a failing Soyuz 1 spacecraft, he brought it into re-entry manually with almost no instrumentation and little ability to control it (an amazing feat), only to have the wildy gyrating capsule tangle it's parachute lines and impact the ground at high speed.
The BPRS would be considered a valid option, if the only other option was hitting the ground with no braking at all.
Deploying the BPRS in a storm would be essentially the same as making a parachute jump into a storm, subject to the same hazards, such as gusting winds collapsing the chute.
The only safe option for a light aircraft is to avoid storms completely.


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Why the need to use right rudder during stall recovery?
Can someone elaborate on why the right rudder is needed during stall recovery for a small single engined training plane like cessna C152 or C172?
Some possible answers are:
A. When recovering from a stall, you need to add power. The increased power induces a torque in the opposite direction.
My problem with this answer is that torque will result in roll and usually ailerons are used to control the roll. Why rudder in this case?
B. This could be to counteract the P-Factor
Since the airplane is pitched down, the ascending blade on the left side will have a higher angle of attack and will produce more thrust, resulting in a yaw to the right. This should need left rudder and not right?
C. This is a variation of A. Since torque induces roll and yaw is a byproduct of roll, you need to apply right rudder. However, in this case we are not using ailerons, so there is no additional drag which will result in a yaw.
Since this question is causing confusion I am adding steps to reproduce the stall and stall recovery and the point at which rudder control is required. See answer from abelenky below which I think is the correct answer.
Step 1: Get to 3000ft, perform clearing turns etc
Step 2: Add Carb heat, Reduce power to 1700RPM, Add flaps and slowly start descending at 55-60KIAS as if you are really planning to land.
Step 3: Idle the power and increase AOA until the plane stalls
Step 4: As the plane stalls, the nose falls, remove back pressure from the yoke and allow the nose to fall

At this point of time you have successfully stalled the plane

Step 5: Remove Carb Heat, Add full power, set flaps to 20 Deg, apply right rudder
Step 6: As the plane recovers and regains airspeed, remove flaps above 60KIAS
Step 7: Gradually return to 3000ft and resume or retry if you want to.

The question is related to Step 5.

Right rudder is not required for stall recovery, its required to keep co-ordinated flight after recovery.

@Jamiec Yes, I agree. But the question was not a flying question, it was a physics question. I was trying to understand how exactly the rudder helps in keeping the flight co-ordinated.

You wrote:

When recovering from a stall, you need to add power. The increased power induces a torque in the opposite direction.
My problem with this answer is that torque will result in roll and usually ailerons are used to control the roll. Why rudder in this case?

I think you already know that a stall happens when you no longer have smooth airflow over the wings. Because you don't have effective airflow over the wings, your ailerons are not working. (they may be partially effective, or have no effect at all)
You are right that ailerons are used to control roll during nominal flight; but a stall is not nominal, and the ailerons are no longer effective.
The rudder, as a vertical surface, is not stalled the same way that the wings are.  So while it may not be the ideal way to counter a roll moment, its more reliable than the ailerons.

Yes, this is what I have been suspecting. You really don't want to use aileron's in this situation because you want to provide as much lifting surface as possible to recover from the stall quickly. And as you said, even if you were to use the ailerons, they may not be very effective at the low speed the plane is. That leaves the rudder as the only option to provide a counter-acting force.

Someone posted this link in a comment to this question yesterday. It said basically the same thing you are saying in your answer.  Oddly, the comment seems to have disappeared.

I'm not aware that rudder input is necessary for a stall recovery.  It may be used in the slow flight and pre stall segments prior to the stall to counter P-Factor, particularly during a power-on stall, in order to track a straight heading.  The only other use I could think of for rudder use in a stall is to induce a spin, or to prevent inducing one, but that would not be a standard for a typical stall recovery.

No, this is what is actually happening. I went thru this less than a week ago multiple times. The plane does have a tendency to go left and to maintain heading I had to use right rudder.

Well, that's what I described.  During slow flight and pre-stall with high AOA, you're also going to have a lot of P-Factor causing the nose to drift to the left I'd uncorrected with rudder.  As the stall onsets and you begin to recover, adding power and reducing your AOA, the P-Factor should be alleviated, requiring less or no left rudder input.  As you establish your climb at Vy, right rudder will be required again to track a heading, but will be the same as the amount required for best rate of climb.

The rudder is required 'after' the stall and as soon as the power is added in an effort to recover, not before.

Then you are probably applying power quickly at the onset of the stall while still maintaining a high AOA, resulting in a lot of P-Factor and left yawing tendency.  At the onset of the stall, release back elevator pressure while smoothly and briskly adding power.  This should help minimize the P-Factor encountered during the maneuver.

:) If I'm stalled, then the nose is pointing downward and there is no high angle of attack. This is by definition of stall.

@PrashantSaraswat An aircraft can stall with a nose-up attitude, I know a few aircraft that can hold a nose-up in a full stall all the way to the ground if you wanted to. The aircraft also does have a high AoA, you may want to revisit the "definition" of a stall.

No.  An airplane stalls when you exceed the critical angle of attack defined as the angle between the chord line and the relative wind.  This can occur at any airspeed, flight attitude, or power setting.  The airplane can also maintain a high AOA while stalled unless control pressure is relieved, reducing the AOA.  I'd suggest you re-read the Airplane Flying Handbook pp 4-5 thru 4-13 and the Pilot's Handbook of Aeronautical Knowledge pp 5-25 thru 5-26.

@RonBeyer I have updated the question. I don't understand what you are saying. This question is specific to Cessna 152/172.

@CarloFelicione I have updated the question. Considering the amount of confusion it caused, I should have listed detailed steps when I initially asked the question.

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What is the best VFR route to CYKZ (ButtonVille) when approaching from the southeast?
I'm planning my first real life cross country trip from KFRG to CYKZ. But I'm very confused by the Toronto airspace. My main question is around how to approach ButtonVille airport from the south (say from Buffalo).

Option 1: Buffalo - Hamilton - hug the coast and drop from 3500ft to below 1700ft - ask CYTZ tower to transition thru to CYKZ airspace.
Option 2: Buffalo - Hamilton - Burlington Exec ( CZBA ) - Brampton Caledon ( CNC3 ) - ButtonVille ( CYKZ )
Option 3: I have flown from KFRG (Long Island) to N51 ( Solberg, New Jersey). This was done with my CFI who contacted New York Approach, told them where we were going and then the controllers ( we got handed off to several different controllers ) guided us over JFK and on to Solberg. Is this even an option? I don't see an option to contact Toronto Approach on the sectional.
Option 4: Just for the sake of completeness, there is the option to fly over the water, direct. But this is not recommended in single engine planes for safety reasons.

Can someone who has flown VFR to this airport before advise on this?

Not directly related to the question, but I'm not sure that it's legal to land at CYKZ if you're arriving from outside Canada.  According to the Canada Border Security Agency, "General aviation aircraft must land at an approved airport of entry (AOE) during the CBSA's hours of business."  CYKZ is not an airport of entry.  (CYHM is, though, so you could presumably land there, check in with CBSA, and then proceed.)

@MichaelSeifert On the Toronto VFR Navigation Chart ( which I purchased ) CYKZ is enclosed in a dashed square box which as per chart legend means that customs are available at this airport. CYYZ is also enclosed in a dashed square box on the same chart.

My apologies — I was looking at the "AOE" list on the CBSA website.  Looking at the "AOE/15" list, it is in fact listed.  (The "15" means general aviation aircraft with 15 people or fewer.)

Thanks for confirming. Your question planted a seed of doubt in my mind earlier :)

I fly out of CYTZ and know the area fairly well. A few things to keep in mind. If you'd like to transition through CYTZ airspace to Buttonville, you'll find controllers there pretty accommodating. Getting in touch with Toronto Terminal is not a problem, you're not asking to cut through Pearson, but you'll be sticking along the shoreline so I wouldn't worry too much.
I would recommend against flying at 1700 feet. That's awfully low. Here's what I would recommend.
Get a VTA sectional for Toronto. This will have much greater detail for the area as well as recommended VFR routes.
Hug the coastline at 2500'. Contact Toronto Approach at 133.4 before entering the zone. Ask for clearance through the zone to Buttonville via the shoreline and city centre. Follow the coast line until you're about 10 miles outside of City Centre (YTZ). There Approach will transition you to Tower if you're at 2500 or below. They will clear you to Buttonville by staying east of the DVP/404. That's the major highway cutting N/S through downtown, east of the airport. Once you're clear of City Centre, you'll get passed over to Buttonville for your landing. As long as you follow DVP/404, you'll find the airport easily. I believe there's a landing fee as well.

you are a godsend. 133.4 seems to be correct but it is not listed on the sectional. It is however listed in the Canada Flight Supplement and I missed it. I have uploaded the Toronto VFR Navigation chart but it doesn't show VFR routes. Where did you get the chart that you uploaded?

You have a VFR chart but you need the VTA. The VTA is the expanded chart for the local Toronto area and will have a lot more detail

Thanks again. Can you also comment on the departure procedure? When exactly am I supposed to contact Toronto Departure?

I recently flew into CYKZ. The simple answer is that Option 3 is best. Just get flight following and they will eventually hand you off to the Toronto City Center Control. These controllers direct all VFR traffic along the coast. And they are all very nice :)

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Compute great-circle track from longitude
The Aviation Formulary defines Clairut's formula to compute the intermediate track  (bearing) for a GC based upon latitude, but any given GC (ignoring one passing through the poles), crosses a given latitude twice (below the maximum latitude where track = 270 or 90).
For my application I'd easier compute the intermediate track based on longitude, since this will have only one solution, but I'm insufficiently capable at spherical triangle math to re-arrange the available formulae to give that result. Any hints on computing immediate GC tracks based on longitude, or modifying the computation based on latitude to select the 'rising' or 'falling' solution, would be welcome.
For context, this is for a navigation device emulation in a simulator, to show the desired track along a leg. All the other values (eg, cross track error) are provided by existing formulae.

Maybe try this question at https://gis.stackexchange.com/ if you get no answers here.

This is not an aviation question, this is a math question, should be moved math.stackexchange.com.

@James Turner: considering the date of the question, you've surely moved on. If you found a solution elsewhere, you can post it here and get some bonus points for answering your own question. Anyhow, the Aviation Formulary has the answer to your question: it's not Clairaut's Formula. You can find the latitude of ownship position by entering its longitude and the coordinates of the GC endpoints into the "Latitude of point on GC" formula. Then, knowing lat and long of both current position and destination, you can determine the heading to use leaving that point from the "Course between points" formula.

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What are some disadvantages that come with a design like a B-2 spirit bomber?
Here is a B-2 Spirit:

source

Source
Many different things can get in the way with a design like a B-2. Although it has really good stealth and looks, does it have any disadvantages that come with the good stealth and looks?

What kind of disadvantages would this aircraft have of an
airliners design or another bombers design like the B-52 or B-1?
What system does this aircraft use to overcome not having
stabilizers?
Why have only 22 ever been built?

By looks I mean its one cool looking aircraft.

Related. (As many other questions about flying wing)

The main problem with the B-2 Spirit (or any flying wing aircraft, for that matter) is that they are statically unstable.

Source
If the lift vector of the wing acts before the center of gravity (as is the usual case when only wings are considered), any perturbation which results in an increase in angle of attack results in a positive moment about the center of gravity, which further increases the angle of attack an so on.
The only way to control such an aircraft is through computers, which continuously detect any changes in the aircraft attitude and apply corrections as required, as it is near impossible (or incredibly taxing) for human pilots to fly the aircraft.
This is the method used in order to 'fly' the B-2 Spirit in the absence of a horizontal stabilizer. If there is any problem with the flight computer (which is remote) or with the sensors supplying data to it, the aircraft will become unflyable and crash.
Another control issue with the B-2 is that the aircraft has little directional stability with no vertical tail. The swept wing offers some stability, though not in the same level as a vertical tail.

Source
Actually, only 21 of these were built, for the following reasons:

The B-2 is costly; by costly I mean probably the most expensive aircraft ever built. With a total program cost of over 45b USD, each aircraft costs a whopping 2.1b USD (which was caused due to reduction in numbers from the initial 132). Also, the (hourly) operating costs of B-2 are twice that of other bombers in the USAF fleet.
With the dissolution of the Soviet Union, the B-2 had effectively become an aircraft without a mission, as it was primarily designed to penetrate Soviet air defence systems.

Its worth noting that the problematic parts of the B-2 design aren't related to it's stealth aspects (e.g. venting the engine exhaust above the fuselage doesn't really make it a "worse" design, though it does substantially reduce the ground heat/noise signature). Some of the stealth features DO benefit from it being a flying wing however (e.g. the pointed nose & "W" trailing edge are effective radar-scattering features, and the degree to which we see them on the B-2 is possible because it's a flying wing).

Just to emphasize: They cost $2,100,000,000.00 each. That's why there were only 21.

That's about as expensive as a Shuttle, and more expensive than a Nimitz-class nuclear supercarrier (barring airplanes). That's pretty expensive.

If they'd built the number they meant to build they'd only have cost about $500m each, so give the guys a break. ;-)

Flying wing is not necessarily statically unstable. There were plenty of prehistoric flying wings without any computers and they flew just fine. It just takes a correct choice of airfoil (and S-curved one with negative camber near the trailing edge), or, with sufficient sweep angle, a significant negative wing twist.

@Zeus: those prehistoric flying wings had fly-by-wire (well, OK - "sinew") and active stabilization systems which worked together to keep them flying as commanded. Also, in emergency situations mass could be ejected via a port in the rear to improve net lift.

@Bob, no, most didn't. You can fold a paper airplane (nearly all of them are 'flying wings') and see how well it flies without any control system.

My error. When I saw "prehistoric flying wing" I thought of pterodactyls. It was, I think, a perfectly natural mistake. :-)

@Zeus: Most paper airplanes are long slender deltas with a gigantic stabilising keel under the fuselage.

Another instance where the complete nonsense of unstable flying wings is repeated. But it doesn't become true – flying wings can be made perfectly stable. Low damping is harder to eliminate, though.

There are r/c model B-2s that fly just fine, along with the Dunne biplane of the early 20th century.  The B-2, with its swept wings and serrated trailing edge, has enough length to be reasonably stable.  The computers may be more needed for fuel saving "relaxed stability" required for very long missions.  Also, the "gigantic keel" of a paper airplane is little more than vertical stabilizer.  Try making paper airplanes with varying degrees of dihedral and "keel".  Owing to their much greater surface area to weight ratio, these are predominantly aerodynamic creatures.

@NathanTuggy huh?  The last Nimitz-class carrier, USS George H.W. Bush (CVN-77), cost $6.2 billion to build, according to Wikipedia.

If you’re talking about flying wings, which is what a B-2 Spirit is, they offer the following advantages and disadvantages:
ADVANTAGES

Extremely clean design.  The absence of a fuselage, empennage, Engine pylons, etc. eliminates virtually all parasite drag from form and skin fraction drag associated with these structures.  Elimination of all OML structural features outside of the wing optimizes top structure to the pure task of generating lift, offering faster speeds and better fuel efficiency.  To my knowledge, the B-2 is the fastest subsonic aircraft in existence today with an Mmo of Mach 0.95.

Low Radar Cross Section.  Something known since WWII when the German Horton brothers developed flying wings.  Combines with advanced radar absorbent materials, shaping, edge alignment, and some other ‘secret sauce’, flying wings become very difficult to detect on radar.  The B-2 is said to have an RCS ‘in the insect category’.

Reduced airport footprint.  Flying wings are shorter and more compact than conventional airplanes.

DISADVANTAGES

Lateral and directional stability problems due to shifting CL and no tail moment arm.  This can be alleviated using advanced digital flight computers to provide artificial stability.
More complex to manufacture due to their shaping and size.
Unsuitable for transport category aircraft due to impracticality of seating positions not on C/L or emergency egress from aircraft.

As mentioned above a B-2 is a fly-by-wire aircraft and uses digital flight control systems to manage Cp as well as differential spoilerons at the wingtips to provide directional control.  The airplane would be unflyable without them.
The Advanced Technology Bomber program of the 1980s, which became the B-2, originally envisaged buying 132 aircraft as replacements for the existing B-52 airplane.  Development delays and cost overruns resulted in the first B-2s leaving the production lines at around 520 million per airplane in 1990 USD.  With the demise of the Soviet Union in the early 1990s, the major threat the airplane was to counter disappeared.  This combined with dwindling defense budgets reduced the procurement number down to 21 airplanes, which each having to bear more of the development costs, resulted in an average unit cost of 2.2 billion USD, making it the most expensive plane to ever fly from a runway.

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Do quadcopter propellers break the sound barrier?
I recently bought a quadcopter and noticed every time I fly it there is this weird buzzing noise. I have heard this noise on other quadcopters around the same size as mine(4in by 4in). On an airliner turbofan engine you can sometimes hear this weird buzzing sound from the engines, which this sound is the n1 fan spinning faster than the speed of sound and resulting in this loud buzzing sound. So is my little quadcopter motors going supersonic or is it something else?Source:(dynomodels.co.uk)

I cant find good tags for this question. If there is a good tag for this question besides supersonic than please add it to the question thanks.

@mins does that mean length of the blade. If is that I measured 0.5in in lenght of each of the 16 blades.

@Ethan diameter means twice the radius (i.e. the width of the entire circle through which the blades spin.) If you have an even number of blades on the prop, you can measure this as the distance from one blade tip to the tip of the opposite blade. Otherwise, you can measure it as 2 x the distance from the center of the drop to a blade tip.

The "buzz saw" noise from jet engine fans is created by high vibration amplitudes in the blades, not from supersonic airflow. A common cause is aerodynamic flutter creating a feedback loop which excites the vibration modes. This doesn't necessarily occur at the maximum N1 speed. Eliminating these problems can be challenging - for example I was once involved with a situation where less than 1 part in 1 million of the total power output of the engine was "getting into the wrong place" and generating the nasty noise.

Is that your actual quadcopter on the picture?

@mins Yes its the same model

I found this EDF (electric ducted fan) where the rotor tips get up to Mach 0.6. Beyond issues of aerodynamics, you need to consider how much strength it requires to whip around those blades without them exploding. I've blown up cheap 6" props by running them at about 25000 RPM (that's also a tip speed of almost M 0.6, now that I calculate it...and that only cost me about ~$17 instead of $170 for that EDF).

Almost certainly not. Given the comments specifying a $0.5$ inch radius (blade length,) that means the circumference of the path of the blade tips would then be
$$2 \pi \cdot 0.5 \, \text{inches} \approx 3.1415 \, \text{inches} \approx 0.2618 \,\text{feet}$$
To get to the speed of sound (which is approximately $1,126 \,\frac{\text{ft}}{\text{s}}$ at sea level,) that means you'd need to have the fan spinning at
$$\frac{1,126}{0.2618} \approx 4,301 \,\text{Hz} \approx 258,060 \,\text{rpm}$$
Needless to say, that's not happening unless you have one seriously expensive quadcopter.
The buzzing you hear is probably either the frequency at which the motor is spinning or, perhaps, the frequency of some oscillation of the fan blades. Most likely, though, it's just the frequency of the motor/fan.

Each rotor has its own motor, so each prop will rotate a close-to but not necessary the same rate.  This may produce a beat note which could be the audible artifact the OP is noticing.

To give an idea of what 258,000 RPM is: the electrons in the Large Hadron collider are doing about 666,666 RPM (0.00 009 seconds per rotation).

@NateKerkhofs: Isn't that mostly just a function of the LHC's size? I'd expect smaller accelerators to have much higher RPMs, since the track is so much shorter.

@DigitalTrauma Yeah, that's definitely another possibility. In all likelihood, it's a mix of several different things, including the fundamental of each motor, some harmonics, some extra oscillations of the fans (which probably aren't perfectly balanced,) and various interference patterns between all of the above, but a beat is definitely a distinct possibility for the source of the buzzing sound.

@user2357112 Yeah, that's just c / circumference of the LHC. You're right that any particle accelerator will have particle speeds near c and, thus, have circuits per minute almost equal to c / their circumference. Also, as a slight nitpick, LHC doesn't normally (if ever?) accelerate electronics. They primarily use protons and lead nuclei.

Arg. That should say "accelerate electrons," not "accelerate electronics." One would hope that they don't accelerate their electronics. :)

Comparing RPM between X and Y, i.e. a rotor and the LHC, isn't really fair unless you mention the diameter.

@NickT Yeah, there's a big difference between being concerned whether something will reach Mach 1 or not vs. being concerned with how close to c it is.

@NateKerkhofs: On the other hand the speed of sound can be achieved in the LHC at 0.01 rpm, this gives an idea of what is the speed of sound with large diameters (9 km). Now what about a music CD? It can't! It is destroyed before reaching this speed, according to this guy.

@mins If it actually contained sea-level air pressure (I'd assume it doesn't,) Mach 1 would be about 0.75 circuits per minute in the LHC, since Mach 1 is a bit over 12 miles per minute at sea level. Still, the point remains that LHC is very large.

@reirab: Ahhh yes, I took 27 km/mn for 27 km/s. And yes if would be better to restore a bit of atmosphere for the occasion. And some heating.

On the other hand, if the numbers were adjusted to 12" propeller (6" radius), a 12x increase, the motor was a 1000kv motor, and hooked up in 8s, then the theoretical speed at 4.2v per cell would be 1.5x the speed of sound - but this is still unrealistic as the force of the air would significantly reduce the speed, and I am not sure how the engine efficiency relates to the RPM (i.e. does it slow down, or just consume more power) - just food for thought that in theory it is possible for a sufficiently powerful quadcopter propeller/motor combination to break the speed of sound

@user2813274 For 12" diameter, Mach 1 would still be 21,506 rpm. I highly doubt any quadcopter is going to reach that with 6" blades. It's more when you get into 60" blades where you encounter supersonic tips.

@mins kv is not related to power, only related to the speed (1000RPM per volt, which at 8x4.2 is 33.6, so theoretical 33600 RPM) - if I wanted to include power, then the propeller pitch, air density, etc. would all come into play, whereas I wanted to keep it simple so I ignored that and focused only on the unloaded speed

@mins Kv, not kV - confusing constant

@user2813274: Ah that's completely different. I didn't know of this Kv. I'm deleting my previous comments that are not relevant anymore. Sorry for the confusion and thanks for the link.

Nitpick, LHC accelerates protons (which are hadrons), not electrons (which are leptons).

I would add, that since the fans are shrouded, what is probably going on is that the prop is scraping against the shroud. Despite there being a gap between the prop and shroud, keep in mind that the shroud is shaped as an airfoil, producing "lift" towards the center of the prop, and is secured only on the bottom. The prop is some sort of molded plastic from what I can see, and it expands out from centrifugal forces. The result may be contact at high RPM, resulting in buzzing.

It's possible, but I would say unlikely. Supersonic propeller tips really mess with efficiency.
The tip speed of many aircraft propellers is close to supersonic, and if not properly controlled can exceed the speed of sound, but most models don't get up that fast (and your blade tips don't have to be supersonic to be annoyingly loud).
There is a formula to figure out the speed of the blade tip. For your quadcopter multiply the blade RPM by the diameter (in inches), and multiply that by 0.00426
$ TipSpeed = RPM * Diameter * 0.00426 $
The result is in Feet per Second.
Anything over 1125 feet per second (343 meters per second) and your tips are supersonic.
Anything over about 650  feet per second (200 meters per second) and the propeller is probably really loud and annoying.

Can you provide this equation in meters too? Thanks!

How do I find blade rpm

@GabrielBrito As a Lazy American it would be easier for me to convert meters to inches (multiply by 39.36) and plug it into the formula I know

@Ethan ...the usual way is with a tachometer.

Its pretty loud so it must be over 650 feet per second. It also shoots up in the air at full thrust so it has to be over 650 feet per second.

@Ethan With a 0.5" blade length, that's extremely unlikely. See my answer. I've updated it to reflect the 0.5" blade length you mentioned recently in a comment.

@reirab I just measured the length of the blade. Did I measure the diameter correctly?

@Ethan The length of one blade should be the radius (assuming you measured blade length from the center of the prop to a blade tip.) The diameter is twice the radius, that is 1" in this case, the distance from one blade tip to the opposite blade tip.

@reirab So it is 1 then.

What is this magic number, 0.00426?

@Brad: It's pi divided by 60 and 12. Required to convert rpm to rps, then in to ft. In meters: 3.14 * d * rpm / 60.

@mins Well, it's 3.14 * d * rpm / 60 regardless of whether you're using meters, feet, furlongs, or megaparsecs. :)

@reirab: Yes, if the diameter and the speed are using the same length unit. It was not the case in the answer (diameter in in, speed in ft/s -- so the additional division by 12).

Yeah this happens to be the "convenient" formula for the RC model propellers I used to use. There's a better formula (which also has altitude & temperature in it & has fewer "magic" unit conversions) but I was really lazy & just grabbed the easy formula from their website :-)

Definitely not. I fly a quad with similar-sized props (mine are 2.5 inches diameter), and there's NO WAY those break the sound barrier, even at full power, tens of thousands of RPM. It's actually very quiet. I think you might be hearing something loose rattling around on the quad- check that everything's tightened down, I took off with half the bottom plate hanging off my quad a few days ago, and I heard exactly the sound you're describing. I couldn't see that it was hanging off because I fly FPV, and I had the goggles on. Learn what your quad sounds like with everything secure so you can hear it when something's off- it saved me from busting the bottom plate off during an acro flight.


text:
F/A-18E and F/A-18F Rhinos: What's the difference?
The answer to this question seems intuitively obvious: One is a single seat strike fighter while the other has two crew stations.  But is that all?
When it was under development I judged that the E variant was an upgrade designed to replace legacy F/A-18s in Navy and Marine Strike Fighter squadrons (the Corps ended up never buying the jet and held out for a newer design) while the F variant was intended to be a multi-role replacement for both the duties held by the F-14 and the A-6 aircraft, while providing a optional arrangement with dual flight controls for training.
But from the NATOPS manual as well as other literature on the Super Hornet, it appears that the aircraft are one in the same, save only for the second crew station.  Does anybody know specifically why the USA purchased x number of E models to equip specific strike fighter squadrons (eg VFA-14) and y number of F models for others (eg VFA-2)?

@Steve These differences are between the hornet (C/D) and the super-hornet (E/F), not between the E and the F. The F actually has lower internal fuel capacity than the E as a result of the extra seat.

Capability-wise, an F-18C pilot mentioned there was essentially no difference, though he felt -F pilots would beg to differ. He did a Q and A session on Reddit.com/r/Hoggit yesterday(?). You can ask him. As for rationale, my memory is fuzzy.

I discovered the reasons for this:
First, for Fleet F-18Fs, certain missions, such as flying as a Forward Air Controller require an additional flight officer to handle the workloads associated with the job and have a tactical control station specific to this work.
Second a number of F models are fitted with dual identical workstations and dual flight controls for flight training new strike fighter pilots who will be moving on to a fleet Rhino squadron after their training in this jet is complete.  I believe completion of advanced strike fighter training in the -F model Rhino qualifies you to fly both the -E and -F variants.

[citation needed]

The only major difference between the E and the F is the extra seat and its consequences (lower internal fuel capacity, lower landing weight etc).

Fuel Capacity internal: (F-18E) 14,400
  lb (6,530 kg) (F-18F) 13,550 lb (6,145 kg)

http://www.aerospaceweb.org/aircraft/fighter/f18ef/
(data and own sources on the bottom of the page)
It also has a lower "Carrier Bringback Payload".

Carrier Bringback Payload F/A-18E: 9,900 lb (4,491 kg) F/A-18F: 9,000
  lb (4,082 kg)

http://www.boeing.com/defense/fa-18-super-hornet/#/technical-specifications

Well, obviously there must be some point in having the second seat when it is paid for in fuel capacity and payload and it is still installed (outside of training, but F is not (just) for training). The difference is that some systems are too complex for single pilot to operate, so they can only be used from the 2-seat version.


text:
How does the rudder on the Rutan Long-EZ work?
I wonder if someone can explain how the rudder on the Rutan Long-EZ works. I have an idea that it is the induced drag which yaws the plane.

It's a combination.  There is a lateral yawing force that is a function of the offset between the rudder's lateral lift force when displaced, and the C of G, like any airplane.  The moment arm is quite short so it can't generate a very strong yawing moment compared to a normal tail.
However, the drag produced by the rudder, being way out on the wing tip, magnifies the yawing force as the drag force is added to the direct yawing force to get a resultant force vector which provides a stronger yawing moment than the lateral yawing force alone.
This allows a rudder surface that is smaller than a centrally located rudder would have to be, with the same longitudinal offset from the C of G, that is depending purely on lateral lift for its yawing moment (like with forward-swept flying wings with enormous central rudders a-la Marske, or if the Long-EZ had a rudder where the propeller is).
A useful side benefit of the Long-EZ's rudder configuration is due to the fact that each rudder can be displaced separately (each one is connected to one pedal, and only moves out from neutral and there is no interconnection between them); you can deflect them both outwards at the same time and use them as speed brakes.

Thank you...why i ask is because i am building a LongEz, and there is a rudder modification, and i do not understand the meaning of this. The old is more like a brake, the new is more like a rudder.

You mean the pedal arrangement?  Did Rutan change the design to interconnect them so you can't deploy each side at the same time?

No it is not the pedals, it is the design of the rudder.

You mean they go left and right now???

No, the new rudder is much longer and not so deep, and i think the angle is less...

Ok I was aware that there was a redesign that made them bigger and I think changed the hinge hardware or something like that.  The old one was just hinged at the edge like a door, and the new one has central bearings on horn fittings IIRC, which allows an internal operating rod instead of the little cable that stuck out the side to pull on the surface horn.

Its correct, but the hinges is the same, i think te benifit is that the operation rod is inside. Maybe the rudder has more area because the less angle.


text:
What is the fuel consumption per mile for a full CEO A320?
I’m writing an essay as part of my GCSE HPQ and one of the statistics I need to base my research and answer on is the fuel consumption per mile or kilometre for a CEO A320.
It doesn’t have to take into account onboard weight like pax and luggage (however if there is someone with that knowledge it would be greatly appreciated) and it would be a normal flight, so both engines running around 50% or whatever cruise speed is and there are no faults with the engines.
Preferably I would like to know it on a plane with tip Fences on the wings but if someone knows the answer for blended winglets instead then it will still be greatly appreciated.

Are you running in a strong headwind, or tailwind? Typically fuel consumption is measured per hour, not "per mile"...

Please see this answer and let me know what is missing. The wingtip devices won't make much of a difference.

@RonBeyer I just need a general estimate so still winds and 36,000ft. Thanks for the quick reply!

@PeterKämpf, yes, I’ve read that multiple times however I believe over longer distances it could end up being a big difference that I would ideally not have in my essay. Thanks for the help though.

Airline direct operating costs are expressed as $ per seat mile, which assumes still air, so his mpg requirement is quite expected.

The weight difference between empty and full A320 is > 30Tons. So you can't ignore the weight of pax and luggage (and fuel). Suggest 70Tons Tk-off Wt. Read:  Payload/ Range pg.6 ONLY. Decide whether the fuel consumption you seek is with respect  to Time (Endurance), or Distance (Range),  or  Cost (Money). Charts are provided for all manner of fuel calculations, an account of what you've set out to explain in your essay would give context and make it easier to dig out. Good Luck!

@skipper44 I'd say that should be an answer.

Maybe once James reverts.

@skipper44 thanks for the link, I’ll have a look through and see what it says. Thanks for all the help!

For some general numbers, you can look at the fuel economy tables on Wikipedia. They tell you an A320 flying a 1000 NM flight at typical payload will burn 3.13 kg/km (11.1 lb/mi) of fuel. For a 2151 NM flight, it will burn 2.91 kg/km (10.3 lb/mi) of fuel.
As already indicated in the comments, the fuel burn depends on the payload (and to some extend of course the route length). To get more realistic values, you can use the Breguet equation as shown in Peter Kämpf's answer. When plugging in different values for the payload and flight range (all at 3t fuel reserves), you get these fuel burns:

Since you asked about fuel consumption per distance, we can just divide by the trip distance and get this:

These numbers are somewhat smaller than the numbers from the Wikipedia table. The difference is likely caused by additional fuel burn for the takeoff and initial climb.

Fuel consumption varies somewhat given for atmospheric conditions, total trip length (fuel load), aircraft weight, altitude etc. Also definition of "full" aircraft is somewhat ambiguous. Is it maximum weight, maximum zero fuel weight with unknown fuel load, full pax and no cargo etc... ?
But for A320 CEO, with heavy weight of 70t (max this would give approx. 7500kg fuel load with MAX ZFW load), CFM-56 engines and wingtip fences at ISA conditions FL350 at typical cruise speed of M.78 fuel consumption is 2557kg/hour. Corresponding TAS is 475kts, so in still wind conditions this equals to ground speed of 547 statute miles per hour.
Edit: to answer your question this is 4.67kg/mile.
Edit2: For "full" aircraft with light fuel load, giving total weight of 65t at FL380 consumption is 2385kg/hr. That gives you the range.
Jet fuel weights about 0.78kg / liter.


text:
What are the repercussions of flying an aircraft with an invalid N number on the side?
I have requested a new N number for my airplane a few months ago. Thinking the change would come through I had my airplane painted with the new number. What will happen if I fly it without the number being authorized?

What will happen depends on whether someone is around to notice/report. Fly NORAD in the middle of nowhere and you can expect a different response than if you fly with ADSB blaring in a Class Bravo.

If it's been more than 90 days since requesting the number, you are supposed to call the registration branch, 1-866-762-9434 and figure out what is going on.

If the previous N-number is still valid and it's simply an issue of paint, you can have the painted number temporarily covered up and the old one displayed over it. This is common in new aircraft test flights, international sales, lease returns, etc.

As a controller, if it's a correctly constructed N-number, I'd know nothing. and wouldn't do anything. If you file a flight plan, however, the N-number you use will go into the FAA's database. Keep in mind that if you ask a controller for flight following, a Mode C check, etc., there will be a record, even if it's only "on the tape".
I have no idea whether they would flag an unregistered number, but I can give you some history on an aircraft that flew with an INVALID N-number.
In 2006 (or so, why is this stuff so long ago?), I was working the high altitude sector in the LBF (North Platte, NE) area. I received a handoff on an aircraft with a call sign similar to, but not exactly "N1EP2D", which is an illegal construct (see https://www.faa.gov/licenses_certificates/aircraft_certification/aircraft_registry/forming_nnumber/)
I alerted my supervisor, who directed me to question the pilot. As it turned out, the pilot had filed this deliberately, and on a whim.
The FAA does not do "whimsical".
I instructed the pilot to submit the correct N-number, which he did, and I amended the flight plan. I also instructed the pilot to NOT use the invalid number, and to call our Operations Manager for further instructions.
I heard it was a six-month suspension, although I had no official follow-up.

You cannot fly. Since you changed the N-Number, you no longer have a valid airworthiness certificate (since they are tied to N-Numbers). This isn't just a wrong number on the side issue, you don't have a valid registration or certificate. You have 10 days after getting the registration number on your aircraft to file the appropriate form and receive an updated airworthiness certificate.
As far as what can happen... that depends. The FAA has pretty wide authority to issue fines, revoke certificates, or even impound aircraft. There is no set "you do X, then you get a fine of Y" like for traffic violations.

But who is going to notice?  Even if you fly into fields with a tower, I don't suppose they look up the N-number of every airplane that lands, or FTM even use binoculars to see the number.  Indeed, in my long-ago student pilot days, I probably gave out the wrong number on occasion, when flying a different plane than the one I usually used.

@jamesqf When is the last time somebody verified you had a license and were current before you took off? Just because you don't get caught, doesn't mean that it's any less illegal to do it. Get ramp checked once though... it happens occasionally.


text:
If I'm instrument current in an ASEL, am I also considered current in an AMEL?
FAR §61.57(c)(1):

Within the 6 calendar months preceding . . . logged at least the
following tasks and iterations in an airplane, powered-lift,
helicopter, or airship, as appropriate . . .

I would infer from this that 1) instrument currency does NOT carry over from one category to another but 2) that it does carry over from one class to another within a category. Is that accurate?

Yes, you maintain instrument currency by category, not class. 61.57(c) only mentions class in the glider-specific requirements in (c)(3). The FAA doesn't mention it at all in related legal interpretations.
Note this wording from 61.57(c)(2) (emphasis mine):

A pilot may accomplish the requirements in paragraph (c)(1) of this
section in a full flight simulator, flight training device, or
aviation training device provided the device represents the category
of aircraft for the instrument rating privileges to be maintained and
the pilot performs the tasks and iterations in simulated instrument
conditions. A person may complete the instrument experience in any
combination of an aircraft, full flight simulator, flight training
device, or aviation training device.

See also this legal interpretation, Griffith (2008) (emphasis mine):

Generally, all appropriate endorsements for passing the instrument
proficiency check, which would be otherwise given if the check were
passed in an aircraft, can also be given when one passes the check by
using an FTD, as long as the FTD represents the appropriate aircraft
category for the instrument privileges sought.

It's true that you have to pass an instrument checkride (or at least some specific tasks) in a class before you can exercise those privileges in that class, but that's a one-time thing that doesn't affect how you maintain currency. See this question for more details.


text:
How are fuel tanks tested and certified?
What ground tests are carried out for testing and certifying wing fuel tanks for use in passenger aircraft? Is there any chamber to simulate flight conditions? If so, how is the chamber constructed?

Fuel wing box, do you mean a fuel tank?

Yes. Fuel tank.

By "ground test" do you mean tests that are conducted in the aircraft on the ground, or do you mean tests that can be conducted in the lab, etc.

The exact regulations governing an aircraft's fuel tanks depends on many factors such as type and number of engines, construction material, mounting method, number of passengers, aircraft gross weight, etc.
But a good overall set of requirements is given in 14 CFR 23.965 - Fuel tank tests. It includes such items as pressure testing, vibration, sloshing, inertia loads, venting, duration and number of cycles of each test, etc.
14 CFR 23.967 thru 23.101 - Fuel tank tests provides additional criteria but also includes requirements for components such as access panels, fuel sensors, filters and strainers, lines, pumps, drains, valves, jettisoning, etc.
Other than a visual inspection for leaks and corrosion, the primary field test for an installed tank is to plug all the orifices and pressurize the tank to 2-3lbs for about 10 minutes. Large rubber stoppers that look similar to corks (with a bolt running through them that expands the rubber) are often used to plug the larger opening such as fuel filler openings.

As an example of what ground testing may be conducted, reference this Test Report from the FAA.
In this test, the fuel tanks were inerted with the On Board Inert Gas Generation System (OBIGGS).  Various weather conditions and operating configurations were evaluated to determine Inerting times and effect on oxygen levels in the tank.
Tests that measure the actual fuel quantity of the system are also part of the ground test campaign.


text:
Legal requirements for electronic flight bags like Foreflight or SkyDemon
I’m wondering what the legal requirements to use EFBs like ForeFlight or Skydemon or similar for primary flight planning and navigation. If I remember correctly, I once heard about requirements on battery percentage, backup device, external battery or similar.
In particular, I’m interested in the situation in Germany, but I’m happy to hear about differences to other countries (e.g. FAA vs. EASA) as well. I’d be happy about hints on where to find regulations like these as well.

These are portable devices that are not permanently mounted on the aircraft, so there are no regulatory requirements. It's up to you to make sure you have enough power, and if you run out, to be able to use your aircraft's normal navigational systems.

This question has some related information about the US

you actually have two questions here

...for primary flight planning

EFB's with up to date charts are legal for planning and reference as covered in this question.
Many EFB's (well at least foreflight that I know of) here in the US allow you to file flight plans, and receive briefs from a weather briefer right in the system.

...and navigation

EFB's are legal for navigation as you would use a map but they are not legal replacements for GPS/AHARS units despite the features they have. Simply put they are not TSO'ed and not legal navigation instruments.
This is also spelled out in the regs directly

The EFB system does not replace any system or equipment (e.g.
  navigation, communication, or surveillance system) that is required by
  14 CFR part 91.


text:
Can someone identify these drop tanks?
I was wondering if anyone can help me identify either of these drop tanks?  The one in front in the top photo measures about 11' long.

(Source of second photo-- this related ASE question)

Do you know where it was found? That would be useful.

I'm going with tip tank for a Lockheed P-80 Shooting Star.

The teardrop tank was already answered for, so I’ll just field the second half. The blue tank looks like one produced by Firestone (same outline, same seam, same filler and even similar appearing attachment points) - shown here (source https://usautoindustryworldwartwo.com/images/Firestone/maps-droptanks-107w-1.jpg)
Addendum - these appear to have been used on P-51s per this link (I won’t embed the images being unsure of the usage rights):
http://www.sim-outhouse.com/sohforums/showthread.php/67664-quot-FF-902-quot/page2?p=718648&viewfull=1#post718648


text:
What makes Airplane Fly? Does Bernoulli Principle still Reliable?
Even the earliest airplanes did not apply Bernoulli principle. The wings were flat, and it worked.
An honest engineer admitted that 'take off' is a mystery. Is there alternatives for Bernoulli principle?
To me Universal Acceleration under Flat Earth model is the one and only convincing concept to explain flying phenomena. It fits reality and experiment. Throw a flat, circular objects horizontally, the more speed the more altitude. The ascending air hit the underneath parth of the object.

Welcome to Stack Exchange! Have you read the answers to "How do wings generate lift"? If not, I recommend reading through those, and those may answer your question. If you have already read those, can you be more specific about which part you'd still like to understand?

The answers on this question might also help you: How does Bernoulli's principle contribute in lifting airplane?

@Tanner Swett thank you for the link. I have editted my post.

A simple overview is here: https://www.youtube.com/watch?v=PF22LM8AbII

This is a joke right?

Again, to fly, with just flat wings, it works. The point is not at the wings shape. It's the Wings Area and the entire underneath of the airplane's body.

If the joke has evidences, it's not a joke.

The early wings weren't flat, they were just thin.  They still had camber.  They were more or less going by bird airfoils in the early going.  In the end though, the way it works is, you're an air molecule sitting there minding your own business, then a wing comes along, lifts you a bit, then shoves you down much harder (or more correctly, induces you to move down by the changes in pressure), trying to keep itself from falling, and you find yourself lower than before.  The work done to move you there is lift.

@Danang Tyasworo with enough power no wing is needed at all (rocket).  Flat objects will fly.  The wing makes them easier to fly.  So the bird does not need a rocket to fly.  Much can be learned from them.

@DanangTyasworo Universal acceleration is a ridiculous model that violates the very existence of an atmosphere that we experience. The fact that static pressure is higher towards the ground, and the fact that there is such a thing as static air with zero dynamic pressure, are evidence enough that this model is garbage.

@Jimmy Hmmmm. I think that the universal acceleration hypothesis is false, of course, but I don't think that the reason you gave for its falsehood is correct. In any case, the comments on this question aren't the place to discuss that; if you're interested in discussing it, please take a look at what I just sent to the chat channel: https://chat.stackexchange.com/rooms/12036/the-hangar

Yes I've noticed the same happens when I just stretch out my arms.  The ascending air hits the undersides and I go zooming up!

@quiet flyer You reminded me something I did in my chilhood: streching out my arms out of the car's window. Regardless it's an arm or anything else with any shape, flat or round, there is gonna be zoom up effect.  Speed gives force upwards by the ascending air. The more speed the more air drive up force. Even when you speed a car, there will be a bit 'flying' sensation (the real one). When the car decreases the speed, the weight will get back to normal.

@Tanner Swett So sorry, that chat channel requires 18 reputation so I couldn't join the chat.

This just makes no sense.  Let's say we have a huge enclosed elevator rising at 100 mph.  If we drop a parachute or throw a paper airplane within the elevator, does it take longer for it to hit the floor of the elevator than when the elevator is at rest?  No.  Now say the elevator is ACCELERATING upwards.  Now it takes LESS time for the parachute or paper airplane to reach the floor of the elevator than in the other two conditions, because apparent gravity is increased.  So your supposed observations wouldn't support your theory even if they were actually accurate observations.

@quietflyer I think the tools for experiment should be the real one. Please give me a video link.

Earth is the real experiment.  Due to earth's rotation around sun, the ground has an upward velocity of thousands of miles per at most locations near sunrise, and a similar downward velocity at most locations near sunset, yet we see no unusual changes in the sink rate of a gliding aircraft.  As for effects      of acceleration, it is obvious from nasa "vomet comit" experiments that things float with zero downward acceleration relative to room when room is accelerating earthward sufficiently fast enough-- coversely we know from basic math that

Conversely we know from basic math that an increase in apparent gravity due to upward acceleration of a container will increase both the airspeed and the sink rate of a glider flying within that container.

I'm not sure that I completely understand what you're asking, but I'll try to answer your question as you've written it, and we can go from there.

What makes an airplane fly?

That question has been answered pretty thoroughly here: How do wings generate lift?

Is Bernoulli's principle still reliable?

Yes, it's a law of physics that explains experimental results very well.

Are there alternatives to Bernoulli's principle?

It depends on what you mean by "alternatives."
Are there alternative explanations that can be used in addition to Bernoulli's principle? Yes, those are explained at "How do wings generate lift?"
Are there any alternative laws which might be true instead of Bernoulli's principle? No, experimental results show that Bernoulli's principle is the correct description of what it describes.
Finally, you didn't ask a question about this, but I'll respond anyway:

To me Universal Acceleration under Flat Earth model is the one and only convincing concept to explain flying phenomena.

For posterity, "universal acceleration" is the hypothesis that there is no gravity; instead, the ground is accelerating upwards at $1\ g$.
For people on the ground and for aircraft, universal acceleration and gravity make almost exactly the same predictions, so it can be difficult to tell which hypothesis is correct. Whether you're on the ground or aboard an aircraft, it's essentially impossible to perform an experiment which would give different results depending on which of the two hypotheses is true.
In particular, standing on the ground and throwing a Frisbee won't tell you anything about whether the apparent force of gravity is caused by gravitation or by universal acceleration.

If the airplane goes up vertically, there will be no 'take off effect'. The airplane will just go straight up. If the wings be regarded as the factor of lift, how come the 'light' wings can bear tons of weights?

@DanangTyasworo airplanes don’t tens to go up vertically. And there is no “take off edfect”, the wing produces lift and that’s either enough to climb, stay level or descent. And yes, the wing carries most of the weight of the rest of the plane. I’ll be honest, given your profile description and the way you are asking I think you are trying to “trap” us with a question that can’t be explained so you can get validation for your flat earth ideas.

@DanangTyasworo "If the airplane goes up vertically, there will be no 'take off effect'." - What do you mean by "take off effect"? I've never heard that term before, so I don't know what that means. "How come the 'light' wings can bear tons of weights?" - Well, why wouldn't they be able to bear tons of weight? I don't understand the question.

@Justsid "We are watching you" or such is out of context. This is a scientific forum. Stick to the topic, not politics.(even tough you have editted your post, this post is still relevant)

This makes no sense. If the ground is accelerating and not the air, then pressure will no longer obey the hydrostatic equation. Super easy way to debunk...

@Jimmy Either the ground and the air all accelerate.

@Jimmy I'm not sure what you're saying. If the ground were accelerating, then it would push on the air, causing the air to accelerate as well, thereby causing the atmosphere to satisfy the hydrostatic equation.

@danangtyasworo no, still violates the observation from hydrostatics. If they accelerate upward, then we will see pressure inversion and not the standard atmosphere.

@Tanner Switt, take off effect = climb. The lighter wings would be broken if lifting up the airplane's body, and passengers etc. So sorry I didn't go to physics school. Just an enthusiast.

@tannerswett no, the reason hydrostatics exist is because air is experiencing a constant acceleration. If only the ground us accelerating, then hydrostatics is bunk.

@DanangTyasworo I realize that it was highly off key and I’d like to apologize. It was pretty immature on my part, hence why I edited that part out.

@DanangTyasworo "If the airplane goes up vertically, there will be no 'take off effect'." "take off effect = climb" If an object (airplane or otherwise) which is moving vertically is not either climbing (as in: increasing its height above a reference level, such as the mean sea level) or descending (which is not the usual thing to do around takeoff, though it does happen on occasion), then what is it doing?

@DanangTyasworo "The lighter wings would be broken if lifting up the airplane's body, and passengers etc." - No, wings are more than strong enough to support the airplane's weight. This is sometimes tested by flipping an airplane upside down and loading the wings up with sandbags; the weight that the wings can support is much greater than the weight of the airplane.

@Tanner Swett "wings are more than strong enough to support the airplane's weight" Unfortunately, I still can't convince it.

@JustSid That's okay.

@a CVn if an aircrat/militery jet goes up vertically and there is no any curved trajectory because there is no force from horizontal directions. The force comes only from below.

@Jimmy The force comes from the universal acceleration. It even doesn't make sense to claim lift phenomenon under gravity theory. The force is not downwards, it's upwards. Gravity never been proven, even when you stand, walk and run smoothly, without any difficulty, that means you've debunk gravity. The ground has no magnet effect.

@Danang Well, I don't know what to tell you. If you ask me a question, and I give you the answer, and you say "Unfortunately, I still can't convince it," then I don't know what else I can tell you that would be useful to you.

@TannerSwett Just saying: nowadays the education system and things related to it, are full of scams. We can't obtain the truth easily by just reading books or watching videos. We must heavily struggle to figure out anything in the world.

@DanangTyasworo -- see https://aviation.stackexchange.com/questions/67049/would-all-these-three-things-have-the-exact-same-effect-on-the-observed-flight-b


text:
What was the first jet-powered supersonic aircraft?
Just to clarify: I am explicitly not referring to the Bell X-1, or any other early experimental supersonic aircraft that were rocket-powered. I'm curious as to the first supersonic aircraft powered by an air-breathing jet engine, as well as (if possible) the technological innovations needed to transition from rocket-powered to air-breathing supersonic flight.

in level flight? Or during a dive?

@rul30 I meant in level flight. Thanks for the catch!

One ME-262 Pilot claims to have exceeded Mach 1 in a dive, but the conditions are disputed due to compressibility and later tests that find the aircraft uncontrollable above Mach .84. The first U.S. fighter plane to exceed Mach 1 in level flight is the F-100 Super Sabre.
For research on how the sound barrier was broken as it results to aircraft design is to read Wikipedia: Sound Barrier.
Wikipedia also has a good read on Supersonic Aircraft that lists aircraft by manufacture date.
As for technological innovations, I would suggest reading about the turbofan engine, specifically inlet design since the air must be slowed sub-sonic before entering the compressor stages.

It appears, from your "Supersonic Aircraft" link that the F-100 was manufactured in 1953. The MiG-19 was also built in 1953, while the Saab 32 Lansen was manufactured in 1952, and the Convair XF-92 was built in 1948. Was the F-100 the first to attain stable Mach1+ level flight?

The F-100 is the first American aircraft to sustain Mach 1+, and as far as I can tell the first fighter to sustain it. The XF-92 was only able to hit Mach 1+ in a dive (and it was a 1-off prototype). The Saab 32 was in development in 1952 but not manufactured until 1955 (plus its top speed was Mach 1.031 on a good day). Really when you get down to it you are probably talking months between a few models so its difficult to nail down which one had it first.

Just wondering since you specifically called out the first US fighter, while the question asked for first. I'm good with your answer and explanation.

@FreeMan for other countries accurate data is often not available (especially the USSR and China come to mind). Dates for aircraft as to first flight, in service date, etc. are often guessed from when the aircraft is first seen and where by spy cameras rather than official documents.

A member of the Century Series, the F-102 was the USAF's first operational supersonic interceptor and delta-wing fighter. (Wikipedia: Convair F-102 Delta Dagger)

Its innovative "coke bottle" fuselage design to lower the drag at the wing root was critical in achieving supersonic flight.

Me at Saigon with my F102

While not capable of level-flight supersonic performance, the Korean War era F-86 Sabrejet was capable of slightly exceeding Mach 1 (I recall the figure as Mach 1.05) in a shallow dive.  This was one of its performance points over the (otherwise similar) MiG-15, which was Mach-limited and became nearly uncontrollable in the transonic regime.
While not generally considered "supersonic" the F-86 was capable of limited supersonic flight, and had several important features that were common to later truly supersonic designs -- sharply swept wings and fuselage-mounted drag brake panels, for example.

Legend has it breaking the sound barrier in a dive, unleashing a much louder boom than the climbing X-1 (the sane way to try it).

DH108 (de Havilland) Powered by the 3000lb thrust DH Goblin and piloted by John Derry 6th Sept 1948 achieved Mach 1.07 in a dive.
According to an account published in "The Evening Star", Washington, DC (Sep 10, 1948), p. A-19:

In 1948, the Royal Aero Club awarded John Derry the Gold Medal for being the first British subject to exceed the speed of sound.
For more information, see Brian Rivas and Annie Bullen, "John Derry: The Story of Britain's First Supersonic Pilot" (1982)

Welcome to Av.SE. Can you provide a link to this incident so that an interested reader can verify it & learn more about it?


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Is it legal to make a non-military stealth plane?
Just as military camouflage can be legally worn by civilians on most jurisdictions (e.g., in the U.S.), can I create a stealth aircraft for non-military use? More precisely, can I register and fly the thing?

In which country? Keep in mind that USA & the rest of the world are different planets in terms of weapon laws. What is legal in the USA could get you 10 years in prison in an EU country only for possessing it.

Making a plane "look stealthy" and making it actually stealthy are two very different things.

See also The Facetmobile

Just theory, but you may find some of the materials you need hard to get, simply because their only purpose is military use.  In fact, I would expect the vast majority of the surface treatments used are not just hard to get, but actually classified.

I don't know about FAA certification, but I'd bet the DEA would be mighty interested in what you were doing!

Usually people doing "stealthy" stuff are not interested in "registration".

Why would it be illegal? Is there a specific law that specifies the RF reflectivity of an aircraft?

Yes you may, but you need to carry a mode C transponder while above 10,000 ft or in some types of controlled airspace and have it switched on. Which pretty much negates the stealth capabilities of your aircraft.
To quote the linked AOPA page:

According to 14 CFR 99.13, no person may operate an aircraft into or
  out of the United States, or into, within, or across an ADIZ
  designated in subpart B unless operating a transponder with Mode C.
  Certain exemptions might apply to aircraft that were not originally
  certified with an engine-driven electrical system; see 99.13(d).

Any examples of what aircraft have been covered under the exemptions they talk about?

"Which pretty much negates the stealth capabilities of your aircraft." Well let's just say most of it is just for show. Like driving a sports car on speed-limited roadways. :-)

@curious_cat 99.13(d) covers "...an aircraft which was not originally certificated with an engine-driven electrical system and which has not subsequently been certified with such a system installed, a balloon, or a glider." - https://www.law.cornell.edu/cfr/text/14/99.13 It makes sense that you get an exception if you aren't certified to have a power supply to run the transponder!

@Andrew The phrasing made me wonder whether there is such a beast as an "aircraft certified with a non-engine-driven electrical system" Would such a craft be able to run a transponder off whatever drives their power supply? Batteries? Fuel Cells?

@Andrew Also, as an pedantic aside, would one of the recent solar powered craft be excluded technically from the "engine-driven" definition & hence be able to find a loophole for not operating a transponder? Though God only knows why someone would want to do that. But just a hypothetical question.

@curious_cat no idea - but note there's nothing in there saying you can't carry a transponder if exempt, just that you don't have to!

Put another way, I don't think there is any country in the world where flying a stealth aircraft under stealth would not be considered either a de-jure or de-facto act of aggression.  A "non-military" use of a stealth aircraft, therefore, simply does not exist.

@markgarcia - you could just make a plane that looked stealthy but wasn't particularly, if it was just for show...

@curious_cat: plenty of battery electrical systems. Think Piper J-3 Cub. No alternator or electric when built, but you can always run a radio or night lighting from a battery.

@jjack: But this is what a transponder is for. A stealthy airframe will not create the primary echo but still transmit the squawk, so it is visible to the ground controller. Of course, this requires a ground radar which displays a squawk even if it cannot be matched to a primary echo.

Lat and Long are figured out by the rader station from the timing of the transponder reply.

@Andrew: Great, now I'm trying to imagine a stealth glider...


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Why is this missile positioned in this odd position? How can it be launched correctly?

How this missile is positioned here in this odd position? How this can be launched right from this jet?

What "missile" in that picture are you talking about? I don't see any attached to that jet... Are you asking about the ones on the side? Near the canopy?

A freehand red circle indicating what missile you're asking about would add considerable clarity to this question.

I see like 6 different things here that look like missiles or things that could be mistaken for missiles. Which thing are you looking at?

You're seeing the Sidewinder on the folded up wingtip of the F-18 that is in the foreground out of frame except for its wing tip and missile sticking up at the bottom.  The airplane is between the camera and the adjacent F-18 who's canopy is visible.  The long lens being used foreshortens and compresses everything distance wise so it looks like the missile is 6 inches from the canopy when it's actually probably 20-30 ft closer to the camera.

Thanks. Curiosity killed, tranquility prevailed.

This answer is as decisive as a sidewinder!

@keshtopat , don't forget to "tick" correct answers; if you do so it gives you points and allows you to ask more and more great questions like this.

Note that the sidewinder is slightly out of focus (compare to the canopy) - this gives away the foreshortening.  We could work out how much closer from the dimensions in reality vs in pixels (as I suggest in this old answer, but here we've got more to go on)

It's also identical to the same thing on the plane behind it.

@LightnessRaceswithMonica Not quite - the one in the background has a blue stripe, indicating an inert training missile.  The foreground missile has a yellow stripe and brown stripe, indicating a live warhead and rocket motor, respectively.

You can also see somebody's hand in between the missile and the wingtip, just in front of the yellow stripe, so it's presumably being serviced in some way at the moment...

So, essentially this, but from another angle...?

Yes, but I'm really curious to know from where the shot was taken.  It looks like the taxiing aircraft is moving up to the catapult, so the camera is somewhere to the port side of the ship, toward the bow end.  It makes me think it was taken from the rescue helicopter that normally hovers near the ship during cat launches, using a long telephoto lens.

@JohnK The long lens impression is added to by the similar apparent length of the portions of the two missiles that can be seen despite the necessary difference in distance between them. Linear shortening with distance is pronounced when the photo is taken from not far behind the closest aircraft. With a long lens the absolute differnces are not very different so linear dimensions appear similar.

@JohnK, I believe that shot is taken from the island looking forward, and the Hornet is taxiing aft.  It's a little tough to confirm because it is cropped severely, but I think the markings to the left are of the landing area.  Take a look at the photo here for a comparison of the perspective I think this was taken from:  https://www.military.com/daily-news/2019/08/20/e-2d-hawkeye-aircraft-takes-out-4-super-hornets-carrier-repairs-underway.html


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Are the functions of ailerons and rudder similar?
The ailerons help the plane to bank left/right by increasing lift to one wing and decreasing in another. Likewise, the rudder also helps in turning the plane by yawing and deflecting the nose right/left. So their performances sound quite similar(i.e. to make a turn)? Then, why should we keep both of them?Like in a ship or motorboat there is a rudder only and no ailerons.Are ailerons present for quicker operation and rudder for extra support and stabilization only?

Related questions on rudder use in roll and purpose of the rudder.

The answer depends on the dihedral: If there is enough of it, then yes.

Short answer:
Rudder and ailerons have different purposes and control rotation about two different axis. However a rotation about one axis induces a usually unwanted rotation on the other one. In order to rotate exclusively about the desired axis, the other control must be used to cancel the secondary rotation. This is called coordination of controls.
Rudder and ailerons are not the only controls requiring coordination, elevators and throttle actions must be coordinated too, to prevent a change in altitude to result in a change in speed and vice-versa.
The rudder is mostly used to:

Limit yaw movements for safety (Dutch roll) and comfort.
To force the aircraft in a crab (heading not aligned with course), while the weather vaning effect tends to orient the aircraft with the airflow (e.g. for a cross-wind landing).
To force the aircraft to face the airflow when performing a turn. We'll talk about this below.

See Understanding the use of rudder for a more comprehensive explanation.
Ailerons are used to turn, but for a non-small turn an unwanted adverse yaw, opposite to the turn, develops and moves the aircraft away from the airflow (crab), the rudder is used to cancel this crab angle and make the aileron-initiated turn effective.
The availability of a yaw damper relieves the pilot from the duty of coordinating rudder with ailerons in a turn. The yaw damper controls the rudder for stability purposes, and at the same time it maintains the aircraft longitudinal axis into the relative wind without pilot action.

Detailed answer
While it is intuitive to think a turn is triggered by yawing the aircraft and keeping the wing horizontal (like a car), this method is actually ineffective with a rudder of the normal size. The rudder forces the aircraft to change its heading (yaw) but the flight continues more or less in the same direction, the aircraft now moving crabbed. This is specially true as speed and altitude increase and rudder aerodynamic force becomes smaller compared to other factors like inertia.
Banking turns the aircraft
An aircraft is turned by rolling (banking) the wing. When the aircraft spins about the roll axis, the direction of the lift is changed (A/B below). Like any force, the lift vector can be broken down into components (B):

The horizontal component of the lift moves the aircraft away from its original path and the aircraft turns around some point. (Note the vertical component, which still opposes the weight, is now smaller, and a non-small turn also requires adding engine power to maintain altitude.)
However something quite undesirable happens (C): To roll the wing, the upper aileron has to create more lift than the lower one. Lift is created by deflecting the airflow, and this action has a cost: The disturbed airflow creates 'induced' drag. This drag is different from the other drags, it's not due to the friction or the shape of the aileron, but to the deflection of the airflow by the aileron, and increases with the amount of lift created.
Like aileron lift, aileron induced drag is larger on the upper wing, that is on the outer side of the turn. As there is a drag differential, the wing is no more balanced and wants to yaw on the right, opposite to what we want. This force is known as the "adverse yaw".
A part of the adverse yaw is balanced by the weather vaning tendency of the aircraft, due to the action of the fuselage and the rudder. However this only compensates partially for the yaw. All these forces makes the aircraft turn a bit, but crabbed, as seen in picture D. This situation where the aircraft is not aligned with the airflow is an "uncoordinated turn", it is very inefficient, slows the aircraft and stresses the airframe.
This is were some action on the rudder is required: The pilot adds some left rudder to completely cancel the adverse yaw created by the ailerons and align the fuselage with the airflow (E). Doing this any slip and skid motion is also minimized. This is known as performing a coordinated turn.
As visible on the figure E, the horizontal component of the lift, the one pulling the aircraft towards the center of the turn, is constantly reoriented in the direction of the center, contrary to the case of the uncoordinated turn (D).
Rolling the wing is a very effective way of turning the aircraft, but needs some rudder correction to account for the induced drag moving the aircraft longitudinal axis away from the airflow direction.
Ailerons deflection reduced in the turn
Note that when the desired bank angle is reached, the pilot reduces the ailerons deflection. The excess of lift and drag on the upper wing decreases too, as does the adverse yaw. The rudder deflection can be reduced too.
Normally the aircraft should maintain its bank and continue to turn with ailerons in neutral position, due to the upper wing flying faster and generating more lift.
However the aircraft in a rolled attitude actually slips into the turn and the dihedral effect tends to decrease the roll angle of the slipping aircraft (roll stability). So some degree of aileron deflection will be maintained.
The ailerons (and the rudder) are used to return the wings to their horizontal position and stop the turn more accurately.

Ailerons-rudder coordination
Coordinating turns is part of the basic training for a student pilot as uncoordinated turns are not only ineffective, they are also unsafe:

Some part of the wing or the controls can be in the shadow of the airflow, meaning they have no useful effect to control the aircraft.
Lateral accelerations develop, the aircraft either slips or skids.

The amount of rudder to apply can be determined using (human senses and) different instruments, including the turn coordinator, aka needle and ball Indicator, which is a sort of level (the ball) usually associated with a bank or rate of turn indicator (the needle). The respective position of the ball and the needle according to different uncoordinated/coordinated situations are like this:

(source)

(source)
When executing a coordinated level turn without wind, at sea level, etc, the radius of the turn and the turn rate depend only on the airspeed and the bank angle:

TAS 150kt, bank 20°: Radius 1,676m, 360° in 2:16.
TAS 300kt, bank 30°: Radius 4,227m, 360° in 3:51.

See this question for additional information.
Yaw damper
In commercial airliners, the yaw control is assisted by one or two yaw damper(s) which function is to increase the yaw stability and prevent the development of the dangerous Dutch roll. Thanks to the yaw dampers, the pilot does not need to use the rudder pedals for coordinated turns.

(source)

Other means of controlling roll/lift
A mean of banking wings directly is required, including when Dutch roll and spin start developing and when flying or rolling with crosswind. But bank control can be obtained by other means than ailerons. While ailerons add lift by changing the camber of the wing,

spoilerons combine spoilers and ailerons, and break lift by disturbing the laminar airflow (B-52),

rudderons combine rudder and ailerons on flying wings (B-2A),

and now bleed air and Coandă effect can bank the aircraft without moving surface (Flaviir project).

So, which we use for turning usually, the rudder or the ailerons?

@DwiparnaDatta Both. And you use them both cross controlled for slips and crosswind landings.

I'm not sure if it's used in full-scale aviation (a quick search didn't turn up anything), but some RC aircraft do not have ailerons and use the rudder only to turn, relying on the wing's dihedral to then roll the plane. The roll is then what really makes the turn work.

@DwiparnaDatta It's not either or, it's both, unless you are happy being a lousy pilot.

I would add one small addition to the adverse yaw issue: some aircraft (notably older airplanes, pre-1950, e.g., and sailplanes) require rudder to effect a turn. They develop so much adverse yaw that they'll simply slip through the air with no heading change. A Taylorcraft L-2 I've flown experienced enough adverse yaw that I had to lead the turn slightly with rudder (rudder first, then aileron).


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Does the A-10 Thunderbolt fly without the GAU-8?
Has the A-10 Thunderbolt ever flown without the GAU-8? Can it be done with a ballast in place of the gun? I'm not referring only to the combat role of the A-10, a plane used for training or a ferry flight would also qualify.

Near as I know, the answer to the first question is no. The aircraft requires that a tail stand be fitted to it when the gun, magazine and electromechanical drive mechanism is removed for maintenance.  Operation of the A-10 without the gun would exceed the weight and balance envelope for the aircraft, making flight, as well as ground operations hazardous.
The A-10 has been proposed for use as a converted water bomber to fight forest fires but this balance problem without a counterweight installed in this region would make this very difficult.
http://fireaviation.com/2014/09/25/a-10-warthog-proposed-again-as-an-air-tanker/
If one was going to remove the gun for a ferry flight, it would have to be fitted with some kind of counterweight in its place, which would defeat the original purpose of removing the gun.

You are a bit short sighted in your conclusion. An airframe in need of repair could be returned to the factory, but if the gun was usable it could be placed on another airframe in flyable condition.

@Eric Urban I'm not sure what your point is here.

@EricUrban the airframe could not be returned to the factory as the factory no longer exists. If you mean it could be stripped for depot level maintenance, sure. But it wouldn't be airworthy and would have to be moved by other means (probably truck and/or loaded on a C-17 with the wings removed).

The A-10 has already been used as a fire fighter.   I don't know what mods were made but I know it didn't have a tank killing cannon in the nose.

As I stated above in my answer an A-10 water bomber has only been proposed; no aircraft has yet been retrofitted this way.


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Where can I find the full report of this controlled F-4 fighter jet impact?
I found the following video on YouTube

They used an F-4 Phantom jet as a test article in a crash into a concrete wall at 500 mph. It wasn't actually a crash because the plane was not flying.
I would like to know the disposition of the components of the aircraft if possible. Since this was actually a materials science test and not an aviation test, I am unsure if that even exists. Where can I find the complete report of this controlled impact?

.....somewhere in the New Mexico desert in about a million itty bitty pieces?

I don't think they crashed the report. Just the plane.

"I would like to know the disposition of the components of the aircraft if possible" You want to know where the components ended up? Or are you asking how they were distributed in the "crash" site? What do you mean by "disposition of the components"?

@RonBeyer What I was trying to ask is how they wound up immediately after the crash.

You might also be interested in an NRC Aircraft impact assessment and Deterring Terrorism Aircraft Crash Impact Analyses regarding aircraft crashes into terrestrial nuclear reactors. Some highlights.

The test was carried out by the Sandia National Laboratories under terms of a contract with the Muto Institute of Structural Mechanics, Inc., of Tokyo. The purpose of the test:

... was to determine the impact force, versus time, due to the impact, of a complete F-4 Phantom — including both engines — onto a massive, essentially rigid reinforced concrete target (3.66 meters thick).

The reports on the tests can be found in these places:

Full-scale aircraft impact test for evaluation of impact forces: Part 1, Test plan, test method, and test results by von Rieseman, W. A. et al.and

Full-scale aircraft impact test for evaluatioin of impact force: Part 2: Analysis of results by K. Muto et. al.

Interestingly, the aircraft used in the tests were flyable. The report notes:

A flyable F4D aircraft was acquired by Sandia. The aircraft was modified slightly in order to support the aircraft at four locations with a special carriage structure. ... the aircraft weighed 12.7 tonnes (with some avionics removed). The impact weight was 19 tonnes, which included ... 4.8 tonnes of water that was added to simulate the fuel weight...
The target consisted of a block of reinforced concrete 7m square and 3.66m thick ... with a combined weight of 469 tonnes.

The aircraft was crashed with the engines and only a few parts removed:

A fully functional F4  was used in the impact test.Only the gears and flaps at the main wings were partly removed and replaced by a carriage structure and sleds.

This can also been in the following mass distribution diagram for the aircraft used in the test.

Image from Full-scale aircraft impact test for evaluation of impact forces: Part 1, Test plan, test method, and test results by von Rieseman, W. A. et al.
Finally, the test was for measuring the impact forces, not the strength of the wall, as stressed by Sandia:

At Sandia, a spokesman, John German, said the point of the test was to move the wall, as a way to measure the impact forces. ... as a preliminary step in building a computer model of such impacts, ...
Mr. German said: "That test was designed to measure the impact force of a fighter jet. But the wall was not being tested. No structure was being tested."


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Why is the Eurofighter Typhoon's nose gear door shorter than the bay?
The Eurofighter Typhoon has an interesting "feature" in that the nose gear door is shorter than the nose gear bay itself by a good few inches, as shown here:

Can anyone shed any light on the reason for this gap?  It isn't a simple case of the aircraft in the photo having a maintenance issue, as this gap is consistent across all aircraft tranches and customers.

Maybe a budget cut?

related: the aerodynamic effects of such gap.

Uh oh, looks like someone mixed up metres and yards again!

Looks like no one else out there knows either. Some say it is APU others say some other stuff, but no one knows for real.

@SMSvonderTann thats why I asked here :)  I have asked on several aviation forums and no one knows the answer, which is a bit odd...

@Moo It might be buried somewhere deep within classified docs. o:)

True, maybe its where the chemtrail exhaust is located

@SMSvonderTann Some say it is APU.  Really?  Where?  People who don't know aircraft design?

Would there be any potential cooling needs? Anything hot that gets routed near enough to the nose gear bay that it can be used for cooling? That seems like a very inefficient heat vent, but that's the only thing that occurs to me.

Ventilation for the gear bay?

From PPRuNE (Typhoon nose gear door question...), it's to evacuate heat created by the proximity with the engine intake (as suggested by @GürkanÇetin).

Some fighters and as well civil airliners have fans ending in the gear bay. To allow for pressure relief some sort of opening needs to be created to vent to atmosphere. Various designs are available to achieve this, like the well known grills or mesh on carbon or aluminum structure skin. Or, just shorten a nose gear bay door if you have no place to accommodate the mesh and suck it through top part (see holes in the top where cables is routed) If you stick your head into a F18 nose gear bay and it is electrically powered, it will be quite noisy. Seems as the Eurofighters have the same design.

A video of the Super Hornet's gear swing and a picture of the Super Hornet's underside seems to support your answer. Specifically, a mesh is visible in the nose gear door in the video, and the picture does not show the same gap present in ymb1's Hornet picture.

@ymb1 - are we looking at the same mesh? In the video and picture I linked, the mesh is longitudinal (on the strut portion of the gear door), which is definitely not present in the F/A-18A Hornet picture in your answer, unless I'm missing somethIng.

Could it also be a vent for tire smoke? Most Nose Gears do not have brakes and therefore utilize some form of fixed resistance pad inside the gear bay to spin down the wheel, since this generates heat and smoke the opening could assist in venting this effect.


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What is the best or most popular way to reduce wing tip vortices on an ultralight operating at 600-800k Re?
What is the best or most popular way to reduce wing tip vortices on an ultralight triplane, operating at 600-800k Re with fibreglass wings ,10 ft wingspan, gap of 2 chord, chord of 2 ft, 0 stagger?

Upturned wing
Endplates
Horner tips
Other?

For a triplane with very short span, it might be worth it to make a kind of end plate fin joining all three wings.  Problem is, the end plate itself will create a lot of drag, so it comes down to whether or not inhibiting the tip circulation with that sort of end plate gives a benefit that outweighs the drag of the plate itself.
If your triplane will cruise at high Cls (low speeds relative to stall) where the vortices are strong, the inhibition effect of the end plates may be net positive (like with winglets on jets).  If the thing will cruise and 2 or 3 times stall speed, I would expect that the drag of the plates cancels or outweighs the benefit.  Which is why it's not done very much even with all those biplanes out there where you'd think it's a no brainer to "wall off" the wing tips.
Beyond that, I'd suggest a triangular "Wittman type" wing tip ( Steve Wittman was a famous air racer, who developed these tips for the Tailwind) which is a good way of dissipating the tip circulation on low aspect ratio wings while providing a little extra area and span with minimum additional wing bending.  That could be the best bang for the buck for your short span application.  They were very effective on the Tailwind.

Do you know if that wing has wash out to avoid tip stall?@John K

No.  The tip looks longer than it really is in this picture and had a negligible effect on the Tailwind's very good low-aspect-rectangular-wing stall behaviour.


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What is the best way to move a touring motor glider over a wet grass surface?
In a flight club we operate an SF-25C (about 480kg empty).
In fall and winter the surface (grass) of our taxiways often gets to wet so if we would move the aircraft we would damage the field and we get insulted by the glider guys for ruining their season. However the runways itself (once reached) is fine all year.
Preparing the airfield itself is not possible because of environmental reasons and because we only rented the field and because the distance we need to travel is about 1km many of the options regarding the airfield are out.
The question is, does anyone have an idea on how to solve this problem? Are there any existing solutions? A special trailer, rc tracked platforms..
Here is a picture of that aircraft (to see the landing gear):
source: https://www.jetphotos.com/photo/8664499

This sounds really dumb, but can't you taxi it there? I presume it lives in a hangar with a hard floor -- in my experience pushing aircraft on wet grass often results in slipping tyres on the grass (and damaged grass as a result) whereas if the aircraft is moving under its own power the wheels tend to rotate.

I think his problem is the taxiway gets so soft that the very small tires on the Falke make deep ruts while rolling.  Balloon tires would be the easiest solution but it would require an oversize nose gear fork, and so much for motorgliding with the drag of big tires.

How far does it need to be moved?  Is there a straight path to the hard surface?

@Jim Worst case about 1km streight.

I'm guessing that as a motorglider the Falke has very small tires, 5.00 x 5 or even smaller.  The "on-board" fix would be to install much larger tires to increase the contact patch area, but that would require a new nose gear fork and really big fairings if you still wanted to preserve some L/D, if you could even acquire the parts.
About the only other solution would be a special towing rig where you pull the plane onto a custom-made low slung platform trailer with large balloon tires and tow it behind an ATV or similar, also with high flotation tires, to a spot where the ground is firm enough.